Navigation systems often include an inertial measurement unit (IMU). Typical IMUs include a plurality of gyroscopes and a plurality of accelerometers. The gyroscopes and accelerometers measure a vehicle's velocity, orientation and gravitational forces. However, typical IMUs suffer from various sources of error in the measurements. For example, source of error can include gyroscope scale factor error, bias, and drift. These errors may be time-varying and can accumulate in the IMU measurements. In particular, a small error in an initial measurement may be propagated in subsequent measurements and combined with additional error or magnified by the navigation calculations. For example, a small error in attitude, such as a 10th of a degree, can push the vehicle hundreds of meters away from its target destination.